1. Field of the Invention
The present invention relates to a rotary encoder which detects a rotation angle of a rotating section with reference to a fixed section.
2. Description of the Related Art
As a rotary encoder of this type, a rotary encoder comprising a graduation disk (rotating section), a light-emitting section for irradiating light on the graduation disk, and a light-receiving section (fixed section) for receiving light emitted from the light-emitting section and transmitted through the graduation disk is known. The rotary encoder detects a rotation angle of the graduation disk on the basis of a signal output depending on the light received by the light-receiving section. In general, in the rotary encoder, when the center of the graduation disk is eccentric from an actual rotating center, or when the graduation disk is not perpendicular to the rotating axis, an angular error is generated. An angular error is also generated due to the size of the graduation interval or graduation errors such as a systematic distortion for the circumference of the graduation disk. With respect to these errors, in Patent Document 1, a technique which arranges a plurality of combinations of code patterns and light-receiving elements on the circumference at almost equal intervals to remove these errors is disclosed.
[Patent Document 1]
Japanese Patent Application Laid-Open No. H6-313719
In the conventional rotary encoder, in order to reduce an angular error etc. caused by an eccentricity, an inclination of the graduation disk etc., the center position of the graduation disk and the inclination must be adjusted, and time cost is very excessive. The adverse affect of this graduation error cannot be easily reduced by adjusting hardware. When the rotary encoder is applied to a surveying instrument etc., the following method must be chosen. That is, an angle is measured a plurality of times, the positions of graduations read in the respective angle measurements are shifted from each other, and the measurement values are averaged (pairs of observations), so that the adverse affect of the graduation error is reduced. A technique in which a plurality of combinations of code patterns and light-receiving elements are arranged on a circumference at almost equal intervals to eliminate these errors is expensive. The number of combinations arranged on the circumference is limited, and adjustment of these combinations disadvantageously requires a long time.